A conventional centrifugal pump for pumping up water is provided with a device, such as a vacuum pump, necessary only for priming. Likewise, various self-priming pumps invented to overcome disadvantages in conventional pumps of such a type are provided unavoidably with a device necessary only for priming, such as a self-priming water tank or an air separator tank.
The present invention relates to improvements in the self-priming centrifugal pumps typically disclosed in Patent Document 1-3 (hereinafter referred to as “Original Invention 1-3” respectively).
The centrifugal pump unit of each of those Original Inventions is characterized by a common passage that serves as both a priming water circulating passage during self-priming operation and a discharge passage during normal pumping operation, which is a distinctive feature of the pump unit of those Original Inventions which is not found in previously known various self-priming centrifugal pumps. And, the pumps of those Original Inventions, with further improvements to accommodate various operating conditions, have shown excellent self-priming and pumping performance.
For instance, the principle of self-priming action that circulates self-priming water by the characteristics of a larger volute and a smaller volute to drive out an air-water mixture produced by vortices generated around rotating impeller blades is elucidated in Original Invention 1. In Original Invention 2, the pump is further improved to attain higher self-priming performance by making the self-priming water rotate so that the air-water mixture is forcibly separated into air and water by centrifugal separation, and by providing a “cavity holder” which holds a tail bottom of a tornado-shaped cavity caused by the rotation of the self-priming water, preventing it from extending and being sucked into the volute of the pump. And, in Original Invention 3, it is intended to solve a remaining problem of an increased resistance of the flow passages caused by the cavity holder. A spiral guide is incorporated in the volute passage in order to suppress the rotation of the self-priming water after the centrifugal separation is finished, so that the cavity holder can be omitted, whereby it is intended to achieve an enhancement of the self-priming performance and a reduction of the resistance of the passage at the same time.
As exemplified in FIG. 22, the structure of the pump according to Original Invention 3 includes a smaller volute v1 and a larger volute v2, formed at diametrically opposite positions in a pump casing 1. A passage area of a spouting passage c2 of the larger volute v2 increases its cross section gradually towards a discharge passage h and forms a self-priming water separating chamber e of an upright cylindrical shape. A spouting passage c1 of the smaller volute v1 extends in a curve and merges substantially tangentially into that chamber e. And, a spiral guide 41, formed in a shape to suppress and substantially counterbalance the momentum of the whirling current of the self-priming water coming from the smaller volute v1, is provided on an inner wall of the lower part of the chamber e towards the spouting passage c2 of the larger volute v2. Meanwhile, a space s1 between an outer circumference of an impeller 4 and the smaller volute v1 at the position from which the smaller volute v1 extends is greater than a space s2 between the outer circumference of the impeller 4 and the larger volute v2 at the position from which the larger volute v2 extends.
At the start of the operation of this pump, a necessary amount of water is supplied into the pump and the impeller 4 is rotated. Consequently, the water is accelerated by the impeller 4 and flows mostly into the smaller volute v1. The water is then spouted through the spouting passage c1 into the self-priming water separating chamber e. Thus, the water supplied into the pump circulates through a circulating passage 4-->v1-->c1-->e-->c2-->v2-->4, and this circulating water draws in air prevailing around the central portion of the impeller 4 to change it into water containing bubbles, i.e., an air-water mixture, which is spouted into the chamber e. This self-priming water (air-water mixture) spouted into the chamber e flows in a whirling current along the surface of the inner wall of the chamber e, and owing to a centrifugal separating effect, the bubbles instantly form a tornado-like cavity t having a shape of an inverted circular cone in the central region of the chamber e. And, because the spiral guide 41 to suppress the momentum of the whirling current of the self-priming water is provided at the point where the whirling current just after finishing the centrifugal separation is about to pass by, the cavity is disrupted at that point and therefore the cavity is prevented from being sucked into the larger volute v2. The centrifuged air is gradually discharged to the outside of the pump, and thus the self-priming action is completed before long. After the normal pumping condition is established, the smaller volute v1, the larger volute v2, and the self-priming water separating chamber e form a normal passage of a centrifugal pump for satisfactory pumping.
Thus, the pumps according to Original Invention 1-3 are extremely practical and useful as self-priming centrifugal pumps with excellent self-priming performance and pumping performance, however, the following problems still remain unsolved in some applications. That is, in applications for the treatment of clean or a high-purity liquid, such as food, pure water, high-purity chemicals or medicinal chemicals, there is the problem of insufficient cleanability, either when the cleaning system is CIP (Cleaning In Place: internal cleaning without disassembly) or COP (Cleaning Out of Place: disassembled cleaning).
Normally, an apparatus used for the above purposes requires, as “sanitary specifications”, not only a flat and smooth wetted surface, but also a structure in which easy CIP, COP, and reassembly can be performed. However, with the structures of the pumps according to Original Invention 1-3, disassembly is difficult, and CIP of wet areas without leaving any shadows is also difficult.
In the pump according to Original Invention 1, the pump has a rather complicated structure including two volutes, large and small, causing difficulties in disassembly work. Its flow passages are also rather complicated, causing difficulties in CIP (Cleaning In Place) of wet areas without leaving any shadows.
In the pump according to Original Invention 2, the problem of the insufficient cleanability has not been resolved in any way. There is, instead, the occurrence of new shadows or bottlenecks hard to clean, such as the one on the back side of the cavity holder, which is caused by introducing the cavity holder to enhance self-priming performance. The system is not always applicable to various kinds of liquids because there is a possibility of clogging due to the bottleneck if particles or masses are mixed in the liquid such as food material.
And, in the pump according to Original Invention 3, while the above-mentioned cavity holder is removed, the spiral guide introduced as a substitute for the cavity holder has many local concavities and convexities, and thus the problem of the insufficient cleanability has not been resolved in any way.
It is widely accepted, in the first place, that forming component parts by casting is the most efficient way to manufacture an apparatus of such a complicated construction. Accordingly, the existence of rough surfaces and blow holes due to the casting process also becomes a major obstacle to the cleanability of the apparatus.
Generally, in a conventional type pump, a pump casing is made by casting in one piece including a volute and a discharging diffuser. As regards the contamination of liquid to be pumped due to particulates dissolving out from minute defects on the casting surface, such contamination is tolerated in a field where a liquid of comparatively low purity level is used. And, in a system where high purity level is required for the liquid handled, such as food and an ultrapure water system, the entire wetted surfaces of the cast component parts are finished by polishing and precision cleaning in an attempt to reduce contamination to a minimum. However, such measures to avoid contamination is not perfect, and, unsolved problems, such as particulates dissolving out, still reside therein.
These problems are caused inevitably due to the structure of Original Invention 1-3, and from a technical perspective pose difficulty in solving. Foremost, if the improvement of various performance as a pump is the main focus, the structural composition of its flow passages tends to become complicated, with the trade-off being insufficient cleanability. Therefore, resolving the aforementioned two problems, that is “self-priming and pumping performance” and “ease of cleaning” at the same time seemed a difficult challenge.